1. Field of the Invention
The present invention relates to electronic means for improving the power factor of power-line-operated inverter-type ballasts for fluorescent lamps.
2. Description of Prior Art
In connection with power-line-operated inverter-type ballasts for fluorescent lamps, it is often important that the power drawn from the power line be drawn with a higher power factor than that naturally resulting with such power supplies.
For instance, without any power factor correction means, the power factor associated with ordinary power-line-operated inverter-type fluorescent lamp ballasts will be on the order of 60% or less. On the other hand, in the most common of all applications of such ballasts, it is important that the power be at least 90%.
The conventional way of improving or correcting the power factor of an inverter-type power supply involves the use of an energy-storing inductor means placed on the power-input-side of the inverter-type power supply, either just in front of or just behind the line voltage rectifier means.
One particular power factor correction circuit based on this principle is described in U.S. Pat. No. 4,075,476 entitled Sinusoidal Wave Oscillator Ballast Circuit; another one is described in U.S. Pat. No. 4,277,726 entitled Solid-State Ballast for Rapid-Start Type Fluorescent Lamps.
However, there are significant penalties in cost, weight, size and/or efficiency associated with the use of this method of power factor correction.
The present invention involves the use of electronic means for effecting the desired power factor correction, thereby obviating the need for said energy-storing inductor means and thereby greatly minimizing said penalties of cost, weight, size and efficiency.